/*
 * Copyright (c) 2022, Peter Abeles. All Rights Reserved.
 *
 * This file is part of Efficient Java Matrix Library (EJML).
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.ejml.dense.row.linsol.lu;

import org.ejml.data.DMatrixRMaj;
import org.ejml.dense.row.decomposition.lu.LUDecompositionBase_DDRM;
import org.ejml.dense.row.linsol.LinearSolverAbstract_DDRM;

/**
 * @author Peter Abeles
 */
public abstract class LinearSolverLuBase_DDRM extends LinearSolverAbstract_DDRM {

    protected LUDecompositionBase_DDRM decomp;

    protected LinearSolverLuBase_DDRM( LUDecompositionBase_DDRM decomp ) {
        this.decomp = decomp;
    }

    @Override
    public boolean setA( DMatrixRMaj A ) {
        _setA(A);

        return decomp.decompose(A);
    }

    @Override
    public /**/double quality() {
        return decomp.quality();
    }

    @Override
    public void invert( DMatrixRMaj A_inv ) {
        if (A == null)
            throw new RuntimeException("Must call setA() first");

        double[] vv = decomp._getVV();
        DMatrixRMaj LU = decomp.getLU();

        if (A_inv.numCols != LU.numCols || A_inv.numRows != LU.numRows)
            throw new IllegalArgumentException("Unexpected matrix dimension");

        int n = A.numCols;

        double[] dataInv = A_inv.data;

        for (int j = 0; j < n; j++) {
            // don't need to change inv into an identity matrix before hand
            for (int i = 0; i < n; i++) vv[i] = i == j ? 1 : 0;
            decomp._solveVectorInternal(vv);
//            for( int i = 0; i < n; i++ ) dataInv[i* n +j] = vv[i];
            int index = j;
            for (int i = 0; i < n; i++, index += n) dataInv[index] = vv[i];
        }
    }

    /**
     * This attempts to improve upon the solution generated by account
     * for numerical imprecisions. See numerical recipes for more information. It
     * is assumed that solve has already been run on 'b' and 'x' at least once.
     *
     * @param b A matrix. Not modified.
     * @param x A matrix. Modified.
     */
    public void improveSol( DMatrixRMaj b, DMatrixRMaj x ) {
        if (b.numCols != x.numCols) {
            throw new IllegalArgumentException("bad shapes");
        }
        if (A == null)
            throw new IllegalArgumentException("Must setA() first");

        double[] dataA = A.data;
        double[] dataB = b.data;
        double[] dataX = x.data;

        final int nc = b.numCols;
        final int n = b.numCols;

        double[] vv = decomp._getVV();

//        BigDecimal sdp = new BigDecimal(0);
        for (int k = 0; k < nc; k++) {
            for (int i = 0; i < n; i++) {
                // *NOTE* in the book this is a long double. extra precision might be required
                double sdp = -dataB[i*nc + k];
//                BigDecimal sdp = new BigDecimal(-dataB[ i * nc + k]);
                for (int j = 0; j < n; j++) {
                    sdp += dataA[i*n + j]*dataX[j*nc + k];
//                    sdp = sdp.add( BigDecimal.valueOf(dataA[i* n +j] * dataX[ j * nc + k]));
                }
                vv[i] = sdp;
//                vv[i] = sdp.doubleValue();
            }
            decomp._solveVectorInternal(vv);
            for (int i = 0; i < n; i++) {
                dataX[i*nc + k] -= vv[i];
            }
        }
    }

    @Override
    public boolean modifiesA() {
        return false;
    }

    @Override
    public boolean modifiesB() {
        return false;
    }

    @Override
    public LUDecompositionBase_DDRM getDecomposition() {
        return decomp;
    }
}